1. Field of the Invention
The present invention relates to agricultural implements such as tillage and seeding implements, and more specifically to lift controls and suspensions for such implements.
2. Description of the Related Art
Multi-sectioned implements typically include a main frame and two or more wing frames hinged to the main frame and movable from a laterally extending position into a narrowed transport position generally over the main frame. The implement includes lift cylinders which raise and lower ground wheels to adjust tool depth during operation in the field, and which raise and lower the implement between working and transport positions. During transport, the cylinders on the main frame usually are locked so the main frame is maintained in a fully raised position. As a result, there is no shock cushioning of the implement during transport. When a large bump or obstacle is encountered by the wheels, a heavy shock load is transferred to the implement particularly when the main frame wheels support the weight of the entire implement. Such shock loads can result in substantial wear and tear on the implement and the towing vehicle. The implement frame, frame supports and hinge structures have to be extremely strong and heavy to bear such loads. When folded to the transport position, the implement has a relatively high center of gravity which sometimes results in unwanted oscillations during towing over irregular field and road surfaces.
A towed agricultural implement is often controlled by an implement control unit (ICU) on the towing vehicle for achieving desired depth control in the field working position, level and attitude control, and lift control across the width and length of the implement. Examples of such control are shown in U.S. Pat. Nos. 5,957,218 and 6,129,157 assigned to Deere and Company. Adding a shock absorbing suspension can be expensive and can significantly deteriorate depth, level, stability and attitude control characteristics of an implement in the field working position and while being raised and lowered between field working and transport positions. Therefore a relatively fixed support system is desirable during field working operations and while the implement is transition between the field working and transport positions.
It is therefore an object of the invention to provide an improved transport system for a towed implement such as a field cultivator, chisel plow, air seeder or the like. It is another object to provide such a transport system which overcomes most or all of the aforementioned problems. It is yet a further object to provide an economical means for providing improved machine suspension during road or field transport without sacrificing precise depth control during field operations.
It is another object to provide an improved transport system for a towed implement which reduces shock loads during transport and which is particularly useful in combination with electronic controls providing lift, level, depth and attitude control. It is another object to provide such a system which provides better implement transport characteristics and yet maintains depth control and implement attitude and level control when the implement is in the ground working position. It is a further object to provide such a system which provides for stable and level lift and lower functions of the implement.
It is a further object of the present invention to provide an improved transport system for multi-sectioned implements having hinged wing frames which fold relative to a main center frame for transport. It is another object to provide such a system which reduces shock loads on the hinges and other frame components in the transport position and yet does not deteriorate depth control characteristics when the implement is working in the field. It is a further object to provide such a system which is relatively inexpensive and which is particularly useful with implements having automatic depth control.
It is another object of the present invention to provide an improved suspension system for a large towed agricultural implement. It is a further object to provide such a system with active suspension control to improve stability during transport and reduce wear and strain on implement components. It is a further object to provide such a system which does not adversely affect implement depth control in the field.
An implement frame supported by hydraulically controlled lift wheels includes an accumulator which is selectively connectable to the lift wheel hydraulic circuit. A mechanical shutoff valve or electrohydraulic control valve is connected between the lift cylinder and the accumulator to control hydraulic fluid flow between the cylinder and accumulator depending on the status of the machine. During machine transport, the valve is opened to allow the accumulator to absorb shock loads as the lift wheels move over obstructions and surface irregularities. The valve is closed when the implement is lowered from the transport position to provide precise depth control functions. The accumulator provides an economical shock absorbing suspension which is activated when the implement is raised and travelling across the field or on the road.
Valve operation can be controlled manually, mechanically by a linkage between the lift system and the valve, or remotely from the towing vehicle by a switch or implement control unit. Preferably, the accumulator is blocked until the implement is in or closely approaching the fully raised position to that stable lift and leveling functions are provided during raising and lowering of the implement between the field working and transport positions.
In one embodiment, the valve between the accumulator and the lift cylinder is a proportional valve electronically controlled from the towing vehicle. Control can be adjusted automatically or manually in response to implement conditions such as implement weight or wing frame position, or to field or road conditions or the like to change the shock isolating characteristics of the accumulator. For example, if the center section of an implement includes a hopper which is relatively full, the proportional valve is operated at a partially closed position to provide a stiffer suspension to better accommodate the added weight. If the frame section is relatively light, the valve may be fully opened to provide a softer suspension.
In a further embodiment of the invention, the proportional valve may also be used to provide active control of the accumulator and/or cylinder in response to rate of change of a position signal from the position transducer or an accelerometer or similar device on the implement, or from a steering transducer on the towing vehicle. The active suspension can increase transport stability, provide better stability during turns, reduce unwanted oscillations, adjust quickly to changing transport conditions, and lessen shock loads and oscillations under extreme road or field transport conditions. A similar hydraulic arrangement including an accumulator can be provided for a weight transfer system on the towing hitch and controlled from the ICU for added convenience and stability. In addition to providing the normal weight transfer functions, a hydraulic weight transfer cylinder can be controlled to reduce or eliminate towed implement oscillations about axes generally perpendicular to the forward direction, combat tractor hop, and provide adjustable hitch cushioning for differing towing conditions.
Other features and advantages of the present invention will become apparent from the following description taken in view of the drawings.